LOSS OF PRESSURIZATION REQUIRES AN EMER DSCNT.

Narrative

CREW NOTICED A MOMENTARY 'ACM EJECTOR ON' LIGHT ON THE ANNUNCIATOR PANEL. ALSO; A FLUCTUATING CABIN RATE OF CLB INDICATOR PLUS/MINUS 400 FT. THE CABIN ALT WAS AT 9000 FT AND HOLDING. IT SHOULD HAVE BEEN 5000 FT PLUS/MINUS. THE CAPT HAD THE FO GO ON OXYGEN AS A PRECAUTION; CALLED FOR CHKLIST AND REQUESTED DSCNT FROM ZBW. THE ACFT; A C-550; WAS CLRED TO 24000 FT. ATC WAS NOTIFIED THIS WAS A PRECAUTIONARY DSCNT DUE TO PRESSURIZATION PROBS. ATC CLRED US TO 11000 FT. PASSING APPROX 34000 FT; THE CABIN RATE WENT TO 3000 TO 400 FPM CLB AND WAS UNCTLABLE. THE CABIN PASSED 10000 FT. MASTER WARN ACTIVATED 'CABIN OVER 10000 FT' ANNUNCIATOR CAME ON -- AND AUTO MASK DEPLOY ON CABIN ACTIVATED. AN EMER DSCNT WAS CARRIED OUT -- XPONDER WAS PUT ON 7700 -- ATC CLRED ACFT TO 8000 FT. THE ACFT WAS LEVELED AT 8000 FT AND THE TRIP WAS CONTINUED TO DEST KSWF IN THE LOW LEVEL STRUCTURE AS IT WAS ONLY 80 NM AHEAD AND A CESSNA CITATION MAINT FACILITY WAS AT THE FIELD. CESSNA FOUND A 10 OHM LEAK TO GND ON THE SQUAT SWITCH AND ONE OUTFLOW VALVE THAT WAS LEAKING BEYOND SPECS. WE ALSO REPLACED THE PRESSURIZATION CTLR AS A PRECAUTION.